I don't think this is specific to RTL, it looks more like a localization issue with any language. Every time I enter the privacy controls section, the screen is initially presented in en-US and then it switches to the proper language.
It is more jarring with RTL because the orientation of the text and carats all flip around, but I see the same basic problem with French and Italian.

Comment on attachment 8578409[details][review]
[gaia] zbraniecki:1134448-privacy-controls-fouc > mozilla-b2g:master
Ok, so someone overengineered lazyloading of l10n.js. It was loading after alameda as a module, while UI with text was inlined, so firstPaint happened way before any localization.
I moved it to defer, because it seems to work without FOUC.

Comment on attachment 8578409[details][review]
[gaia] zbraniecki:1134448-privacy-controls-fouc > mozilla-b2g:master
Nice find Zibi! I think this looks fine to me, but I also think Marta should probably take a look. If we're in a rush to land this though, we could always land first and get a retroactive review from Marta. Thanks!